1. Field
This invention relates to a spoked print wheel serial printer or typewriter having a speed higher than that known in the prior art, and more particularly to one having plural independently driven but cooperatively controlled spoked print wheels with, generally, plural open positions around wheel circumferences, possibly redundant symbol spokes, and a single print hammer per wheel configuration.
2. Description of the Prior Art
Prior art serial printers have included those incorporating spoked wheel print elements, commonly called daisy wheels. Each printer has been equipped with usually one and in a few instances two wheels. Where two wheels have been used, particularly in wide-carriage machines, the wheels can print independently but they cannot be simultaneously active in the same portion of the print line. Usually, at least a substantial part of the full line span is inaccessible to one or the other of the wheels.
The wheels themselves have been variously constructed--reference U.S. Pat. Nos. 4,069,907; 4,106,611; and 4,126,400, for example. Until recently, however, despite the elaborations of hub and spoke arrangements, single-printposition mechanisms described were, in reality, single-wheel units, since all spokes and hubs rotated together and are driven by a single motor. Moreover, all wheel assemblies have been, roughly, of the same overall diameter--about 3" (except for Ricoh 2.4" biplanar wheels), and have, typically, carried between 88 and 96 printing spokes (sometimes called "arms", "beams", "fingers", "laminae", "petals", or "tongues"). Ricoh wheels have 64 spokes, each generally, carrying two symbols. Many of the units described in the patent literature and elsewhere have in fact been heavier and had higher polar moments of inertia than the more simple wheels they were supposed to supersede.
U.S. Pat. No. 4,197,022 to Dollenmayer, however, describes a dual-wheel unit differing markedly from prior configurations. The wheels are coaxially mounted and driven alternately by a single motor. For some relatively protracted period, one wheel is active and is driven through a clutch arrangement by the motor. At the end of a short or long sequence of symbols (the words "characters" and "symbols" are used here interchangeably), the entire wheel assembly is shifted axially by an auxiliary mechanism so as to bring the second wheel into the driven, effective printing position. The second wheel now lies in the printing plane previously occupied by the first wheel. A new sequence of symbols is selected from the second wheel, at which time the axial shift is reversed and the original wheel is again active in the same printing plane. This structure, while providing nearly a doubled set of symbols, in contrast to the 88 to 124 usually provided by a single wheel, contemplates the use of essentially standard wheels having conventional dimensions, numbers of spokes, weights, and polar moments of inertia. A minor modification, the provision of a single auxiliary angular opening in each wheel, is required to provide either clearance from obstructions, including the platen itself, for the wheel closer to the platen, when that wheel is inactive; or, in the case of the wheel closer to the hammer, clearance for hammer action when the latter wheel is inactive.
The sole advantage of the entire arrangement in Dollenmayer is the greatly expanded symbol set. If the symbols of both wheels are freely used, a very substantial speed diminution will result. At best, the net operating speed will always be less than the conventional.
In contrast, if instead of a nearly doubled character set, it is desired to greatly increase printing speed, with a more modest increase in the number of characters, in a machine having a carriage of any length whatever, it is necessary in some manner to greatly decrease the size, weight and, most importantly, polar moment of inertia of each of two or more wheels, each with its own smaller, faster, driving motor, to arrange for their noninterfering co-action, and to distribute the symbols so as to minimize required wheel rotations.